1. Field of the Invention
This invention relates to oculography (i.e., eye movement recordings) and methods and devices for making non-contact measurements of the rotations of essentially spherical bodies. More particularly, the present invention relates to inexpensive, real-time, three-dimensional, video-oculography that utilizes a specialized marker array which is placed on the eye.
2. Description of Prior Art
Precise and accurate measurement of eye rotation is essential for the clinical evaluation and scientific study of vestibular (balance) and oculomotor (eye movement) disorders. Common types of such disorders often result in those afflicted reporting problems with dizziness.
The magnitude of such disorders can be noted by observing that over ninety million Americans suffer from dizziness; it is the ninth most common reason adults visit a primary care doctor. Thirty-four percent of Americans age 65-74 suffer from dizziness significant enough to limit their activities of daily life, making it the third most common medical complaint among this group; dizziness is the most common complaint in patients 75 years and older.
Eye rotation measurements are also important because they can be used in other applications, such as input to various computer systems for assorted purposes: data entry, command and control (e.g., navigation of computer-controlled equipment), communication, and the enhancement of virtual reality-based displays.
The “gold standard” method for measuring three-dimensional eye position is the scleral search coil technique. It involves search coils being either implanted on or affixed to the eye and their orientation identified by subjecting them to uniform, stable magnetic fields. However, even this method can suffer from a number of drawbacks that can affect measurement reliability (e.g., implantation of search coils can restrict or distort eye movements due to eye scarring and inflammation or coil lead tension, the imposed magnetic field can be distorted by metallic objects and by currents flowing in nearby equipment).
These drawbacks of the search coil technique have prompted efforts to develop video-oculographic (VOG) systems for the measurement of three-dimensional eye rotations. See FIG. 1 for a description of the coordinate system and the terminology used herein to describe rotational eye movements.
These systems typically make two-dimensional (horizontal and vertical) eye rotation determinations by tracking the pupil and/or a corneal reflection.
To determine eye rotations in a third dimension (torsional), most currently available VOG systems either track two or more landmarks on the eye or measure and track changes in iral contrast along a circular sampling path. In humans, pronounced iral striations make iral contrast tracking practical, whereas, in animals that do not have pronounced iral striations, it is more practical to track attached landmarks.
However, there are problems with these methodologies and the conventional VOG systems. For example, the quality of data using existing methods is often compromised due to misalignment of the camera with the eye. This misalignment can introduce errors >10%. Reflections of the light source on the eye and/or shading of the landmarks/pupil can produce either loss of the landmark or incorrect calculation of its centroid position. VOG techniques that track the pupil are inherently problematic because the contrast between the iris and pupil is not large. This non-exact demarcation zone makes it difficult to precisely define the pupil region and calculate the pupil centroid position.
Additionally, current three-degree eye measurement VOG systems that track landmarks on the eye employ complex and relatively inefficient algorithms. Most require considerable post-hoc processing of the data collected to enable computation of an eye's torsional movements. Meanwhile, those few systems that provide real-time measurements of eye torsional motions are prohibitively expensive for most clinical and diagnostic applications. Most of these commercial systems are for human applications only i.e. they track the pupil and iral signature. Given the same technological limitations pupil/iral tracking is significantly slower than landmark tracking.
Current methods and devices for measuring three-dimensional eye movements need to be improved by making them: (a) less expensive, (b) more portable so that such measurements can be made other than in only clinical laboratory settings, and (c) faster operating so to enable them to provide real-time measurements which can be more timely correlated for diagnostic purposes with the bodily motions which may be precipitating such eye movements.
The present inventors have been working in this technical field and towards the development of such improved methods and devices for some time. Much of their earlier research is applicable to the methodologies described herein and has been documented in the scientific literature. See for example: Migliaccio, MacDougall, Minor and Della Santina, “Inexpensive System for Real-Time 3-Dimensional Video-Oculography Using a Fluorescent Marker Array,” submitted for publication to the Journal of Neuroscience Methods, Feb. 2004, and MacDougall, “The Human Eye-Movement Response To Maintained Surface Galvanic Vestibular Stimulation,” Ph.D. dissertation, University of Sydney, May 2003.
3. Objects and Advantages
There has been summarized above, rather broadly, the background that is related to the present invention in order that the context of the present invention may be better understood and appreciated. In this regard, it is instructive to also consider the objects and advantages of the present invention.
It is an object of the present invention to provide improved, lower cost methods and devices for making eye rotation measurements.
It is another object of the present invention to provide improved, more portable methods and devices for making eye rotation measurements.
It is yet another object of the present invention to provide improved, faster operating methods and devices for making eye rotation measurements.
It is a further object of the present invention to provide improved diagnostic methods and devices for assessing vestibular and oculomotor disorders.
It is also an object of the present invention to provide improved methods and devices for providing eye rotation measurement input to various computer systems for a wide assortment of applications (e.g., data entry, command and control, communication, and the enhancement of virtual reality-based displays).
These and other objects and advantages of the present invention will become readily apparent as the invention is better understood by reference to the accompanying summary, drawings and the detailed description that follows.